Archaeologists have discovered what they say is an unexpectedly rich lode of prehistoric artifacts on the Chessie System railroad right of way in the District of Columbia, a development that could delay the company's plan to sell the property.

The archaeological investigation is part of an environmental impact study ordered when CSX Corp., Chessie's parent company, asked the Interstate Commerce Commission for permission to abandon the 10.7-mile Georgetown branch line because it is unprofitable. The ICC, which regulates railroads, must decide whether the rail service is no longer needed.

The 10.7-mile branch line was once used to deliver coal to a General Services Administration plant in Georgetown that supplies heat to 120 federal buildings. The railroad now delivers the coal in trucks routed through the city.

Further exploration of the sites where prehistoric tools and pottery were found "would contribute enormously" to the knowledge of the prehistoric peoples who lived in Washington area thousands of years ago, said Janice G. Artemel, of Engineering-Science Inc., the consulting firm doing the archaeological investigation. Many "archaeologically significant areas" of the District have been destroyed by development, making these undisturbed areas on the railroad property an important discovery, she said.

Artemel said her firm will recommend that the ICC make a more extensive study of the sites.

The ICC staff is likely to accept the proposal, according to Carl Bausch, head of the energy and environmental section in the agency's transportation office.

If the rest of the environmental impact statement is completed, the staff might recommend that the commission appprove it with a condition that CSX not disturb the historical areas until the scientists are finished, he said.

Other studies ordered for the environmental impact statement probably will be finished within the next week, Bausch said.

Reports from 18th-century investigators and a Smithsonian Institution archaeologist indicated that this area was populated for thousands of years by several groups. The sites uncovered in the current study confirmed these reports and produced much more evidence than expected, according to Artemel.

Many of the prehistoric settlements were permanent villages, not seasonal or hunting camps, dating as far back as 6,000 years, she said. In making small "shovel tests" about every 100 feet where possible, the archaeologists found as many as 95 artifacts, including spear points, flakes produced when the projectiles were made and sometimes used as cutting instruments, and pottery pieces -- an unusually large number, said archaeologist Elizabeth A. Crowell. They also found "intact surfaces," areas where soil levels have not been disturbed since the early peoples lived there, she said.

The scientists chose three sites inside the District, near Chain Bridge, for more extensive digging. They found that the locations "were occupied over a long period, probably several thousand years, by many different groups," said Crowell. The archaeologists have tentatively set the arrival of the earliest inhabitants at about 3500 B.C.

One prehistoric site was found in Montgomery County, about half a mile beyond the District line, according to Artemel. Inside the District, the investigators found remains of the Foxhall foundry, which was established in 1801 and made the guns and ammunition used in the War of 1812, and of a Civil War artillery position, she said.

Archaeologists say that several of the sites will be eligible for listing on the National Register of Historic Places, a designation that provides some protection in many states that have historic preservation laws.

What should be done with the railroad property is a controversial issue in the city and in Montgomery County. The National Park Service wants to incorporate much of the area into the C&O Canal National Historic Park. Environmental and recreational groups would like to see the right of way turned into hiking and biking trails, and nearby homeowners, particularly along the Potomac palisades in northwest Washington, want to prevent commercial or residential development, which CSX Corp. has said it has considered.

Montgomery County has asked the ICC to turn over 84 acres of the railroad right of way to the county government for a hiking trail and cross-county transit line.

CSX said it is willing to swap the railroad land in the C&O canal part for federal property of equal value elsewhere, but the company and the National Capital Region of the park service have not reached an agreement, a railroad spokesman said.

A CSX official said the company has placed a net value of $ 19.5 million on the entire 123.1 acres it owns in the Georgetown branch right of way.

The environmental statement, ordered by the ICC, is being paid for by CSX, said an ICC official.